rw_cod.c

// Simple program to read and write Class of Device.
// To compile: `gcc -o rw_cod rw_cod.c -lbluetooth`
// To install lbluetooth: `apt-get install libbluetooth-dev`
// Execute with 'sudo'
// Note the original CoD first because it has strict rules, you might need to write it back later.

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h> // for close()
#include <bluetooth/bluetooth.h>
#include <bluetooth/hci.h>
#include <bluetooth/hci_lib.h>

int main(void){

  int dev_id;  // ID of Bluetooth adapter
  int sock;

  // Get Device ID          
  dev_id = hci_devid("00:11:22:33:44:55"); // To know adapter adress: `hciconfig -a`

  // Open Socket
  sock = hci_open_dev(dev_id);

  // Write and read CoD
  int timeout = 1000;
  uint8_t cls[3] = {0};
  int class;
  int ret;
  uint32_t new_class =  0x260420;
  ret = hci_read_class_of_dev(sock, cls, timeout);
  class = cls[0] | cls[1] << 8 | cls[2] << 16;
  printf("Class of Device              = 0x%06x [%d]\n", class, ret);

  // Set CoD
  ret = hci_write_class_of_dev(sock, new_class, 2000);
  printf("Required new Class of Device = 0x%06x [%d]\n", new_class, ret);

  // Check read CoD
  ret = hci_read_class_of_dev(sock, cls, timeout);
  class = cls[0] | cls[1] << 8 | cls[2] << 16;
  printf("Actual new Class of Device   = 0x%06x [%d]\n", class, ret);
  
  close(sock);
  
  printf("OK!\n");
  return 0;
}